Preparation And Characterization Of Cathode Material And Solid Electrolyte For All-Solid Lithium Sulfur Battery

Lithium sulfur batteries are fascinating power sources for their low cost and high energy density which can be used in portable devices（taking mobile phones,drones,and autonomous robots for example）and new energy electric vehicles.However,there still exists many obstacles for the commercial development and practical application of lithium-sulfur batteries,such as the insulation of sulfur and polysulfides,the shuttle effect of polysulfides,the volume change of active materials during charging and discharging,the leakage of the liquid electrolytes which might cause fire or even explosion.Based on the fact that the cathode material mainly determines the energy density of lithium sulfur,a large amount of research has been devoted to develop the cathode material.It has been greatly inspired that solid electrolytes have been developed for their efficient and safe application in lithium-sulfur batteries which can be used as a substitute of the liquid electrolytes to improve the safety of the battery and the energy density of the battery.A lithium-sulfur battery with a solid electrolyte is called an"all-solid lithium-sulfur battery."This thesis focused on the preparation of CeO₂ modified carbon aerogel cathode material and the preparation together with characterization of solid electrolyte Li₇La₃Zr₂O₁₂（LLZO）.The main contents of the study are as follows:（1）A carbon sulfur cathode material was prepared by cerium oxide-modified carbon aerogel composite material which was composed of carbon as the main body and carbon fiber felt as the support.The high specific surface area,high porosity,and three-dimensional network structure of carbon fiber felt contribute the improvement of the sulfur load and the conductivity of the cathode.It has shown that the proper amount of CeO₂modified carbon aerogel can also Suppresses the loss of polysulfides and promotes redox reactions.CA/S-3Ce electrode which is prepared by a 2.14 mg/cm² sulfur loading with an addition of 2.76 wt%CeO₂,manifests a high initial capacity（the initial discharge capacity at 0.05 C rate was 1487 mAh/g）and good reversible cycling（the discharge capacity at 0.2 C rate after 150 cycles was 959.13 mAh/g and the discharge capacity at 1 C rate after 100 cycles was 802 mAh/g）.（2）LLZO was prepared by using a new solid-liquid compound method,which is a combination of wet chemical method and solid state reaction method.In the preparation of LLZO powders,the p H value and the molar ratio of acrylic acid to metal ion（L/M）are the main factors affecting the phase of synthesized powder and the properties of LLZO ceramics.The cubic powder of an ellipsoidal shape in a particle size of 2-4μm with good neck connection was obtained with a condition of p H=3,L/M=0.35 and calcination temperature of 800℃.The obtained LLZO ceramics are sintered at 1100℃for 6 hours after powders pressing,with a relative density of94.1%and an ionic conductivity of 3.09×10^-4 S/cm.